1. Field of the Invention
The present invention relates to the field of plant breeding and, more specifically, to the development of watermelon line WAS146-4197.
2. Description of Related Art
Watermelon, Citrullus lanatus (formerly Citrullus vulgaris) is of the family Cucubitaceae. Watermelon produces a fruit known called a pepo, which has a thick rind (exocarp) and fleshy center (mesocarp and endocarp). However, consumers typically consider the watermelon fruit a type of melon because it has a smooth, green and/or yellow exterior rind and a juicy, sweet, usually red to yellow, interior flesh. In the United States, Georgia, Florida, Texas, California and Arizona are among the largest watermelon producing states, but approximately 44 states grow watermelon commercially. Watermelon is typically consumed fresh, and can be used to flavor drinks and/or smoothies. Watermelon is approximately 92% water by weight, which is higher than almost any other fruit, and is low calorie while having high nutritional value. For example, a one-cup serving of watermelon provides approximately 50 calories and 14.6 mg of vitamin C. Watermelon also provides significant amounts of vitamins A, B6, and B1, as well as the minerals potassium and magnesium. Certain watermelon may also be a source of the antioxidant, lycopene.
Watermelons are natural diploids, referred to as 2N (N=11), with chromosomes arranged in pairs. Many plants, including watermelons, can undergo a duplication of their entire set of chromosomes and exist as tetraploids, referred to as 4N (4N=44). Watermelon tetraploids can be produced routinely in the laboratory using cell biology techniques.
A tetraploid (4N) female parent can be crossed with diploid (2N) male parent to produce triploid (3N) seeds (3N=33). A hybrid triploid plant produces watermelon fruit which is seedless. Although triploid plants do not usually produce any viable seed, small, white, rudimentary seeds may develop within the fruit and can be eaten with the fruit, as in the case of parthenocarpic cucumber. The number and size of the white, rudimentary seeds varies with the variety. Occasionally a dark, hard seedcoat or a true seed may be found in a triploid watermelon.
A tetraploid seed parent typically produces only 5 to 10% as many seeds as a typical diploid plant. Commercial seed production of a triploid hybrid cultivar requires a substantial amount of seed for a commercially viable product.
Tetraploid parental lines generally have a uniform or “solid” colored rind, i.e., a rind pattern that is primarily one color as opposed to a rind pattern having striping. Generally, the rind of the fruit from tetraploid parental lines has a light green to a creamy green color. This color is also sometimes referred to as “gray.”
Historically, seedless watermelons commercialized in the United States and around the world involved creation of triploid hybrids by crossing tetraploid line having a light green rind with a diploid line having a striped rind. Light green rind color is a recessive trait when crossed with a stripped rind. However, in the creation of triploid watermelons by this method, the hybrid will receive two doses of the light green rind gene and one dose of the gene for stripes. The rind pattern of the triploid hybrid although striped, has a faded pattern that may not be perceived as fresh. One advantage of crossing a (preferably) round light green tetraploid and an elongated striped diploid is that it is easy to visually distinguish the inbred lines from the hybrid. One means to obtain a darker-striped triploid watermelon is to use a striped inbred tetraploid crossed to a striped inbred diploid line. However, a drawback to this method is that it may be challenging to visually discriminate between the inbred tetraploid (seeded) and the triploid hybrid (seedless).
There remains a need for improved diploid watermelon lines with good yield, dark rind coloration, small seeds, and a readily distinguishable appearance which can be used to produce triploid fruit which have traits such as, for example, dark stripes, red flesh, small seeds, and high nutritional value.